The present invention relates to a procedure for the preparation of endless sheets coated with a prepared coating for printing using non-impact, thermal transfer printers, and which are also phosphorescent when activated by light containing wave lengths of between 440 and 640 nanometers, as well as to the sheet so constituted.
These sheets are designed for use in the manufacture of adhesive postage stamps and seals which must be obliterated (rubber-stamped) by automatic obliteration machines. The said sheets may then be bonded on their reverse side with damp-reacting adhesives or self-adhesive materials so that they can be applied after printing and punching onto the letters or objects to be sent, according to postal or other requirements, in a manner customary up until the present in the sending of correspondence and bulk franking.
Currently, postage stamps are manufactured by two different methods:
1) Via thematic motif printing according to the series, together with the face value of the same.
2) Via printing of the thematic motif, on paper prepared for non-impact, thermal transfer printing which allows the possibility for the franking value to be post-printed using non-impact, thermal transfer printers at the moment of franking when the weight and destination of the correspondence to be franked is known.
On the other hand, in both cases, to invalidate the stamp once the letter or similar has been franked and to ensure in this manner that the stamp may not be used again for the same object, it is stamped with inks via a rubber stamp. This process receives the name of obliteration.
The obliteration process may be manual or automatic.
The manual obliteration process demands that an employee from the Post Office or similar entity manually stamps by rubber stamp all and each one of the stamps that have been affixed to the corresponding envelopes.
The automatic process necessitates automatic stamp detection, in such a manner that the stamp""s position on the envelope is known in order to be able to obliterate or stamp it automatically. For this purpose there currently exist machines capable of fulfilling this function based on the stamp emitting phosphorescent light so that its exact position may be detected.
It has been demonstrated that non-impact thermal transfer printing greatly facilitates the franking of correspondence, and allows the use of self-adhesive stamps with a face value printed in the act of franking, this entire process fusing with the possibility of automatic obliteration with the object of invalidating the stamp once it has been used.
The technique of the invention claimed in this patent solves the problems of franking and the automatic obliteration of stamps and seals performed on sheets prepared for non-impact, thermal transfer printing, used in the sending of correspondence or parcels. The present invention unites in a single paper or synthetic sheet the following properties:
1. That the said sheet is printable by non-impact, thermal transfer printers so that the franking value or other logotypes may be printed on it.
2. That at the same time it is phosphorescent so that it may be obliterated automatically.
Also, at the same time, this processed, paper or synthetic sheet may be printed using any of the traditional printing methods: Offset, Gravure-printing, Flexography, Transfer, etc. to create the non-variable motifs on the adhesive stamp.
The coat to be applied on the sheet consists of some lactone or spiropyrane type colorings or iron metallic complexes that react with weak organic acids to produce the coloring when heated via a thermal head, as well as activators to accelerate the said reaction. Also absorbent materials and charges to absorb the resulting fusion products. Moreover, it contains an inorganic phosphorescent pigment of the ZnS:Cu type of the appropriate particle size to produce phosphorescence in a pre-specified time and wave-length.